Weight capacity of concrete floor?

[sandspider]

Hi all

 

We have a conservatory (built a good while ago, not quite sure when) which has a concrete floor, about 6" thick I think. Probably compacted hardcore under there, then straight onto the soil - not sure about this, will have a dig around outside when I get a chance. There is underfloor heating in the slab, and tiles on top. My wife wants to put a framed swimming pool in there, quite big - which will weigh about 7500KG when full! Is this going to be too much for a 6" ish concrete floor? The pool is 4.5 x 2.5m, so the weight should be spread quite evenly. And the same pool was fine in the garden, straight onto the soil - but might it crack the slab or something if it's not evenly poured?

 

Thanks.

[Centrepin]

Concrete generally is laid at 100mm,  4" in real money and weighs rough 2.4 tons per cubic metre. Could be compacted hardcore or even block underneath, more likely to be a sheet of visqueen between layers as damp proofing. Generally conservatories are laid visqueen over bare earth, depending on price/builder and corners cut.

If it's underfloor heating it will be totally differant with a breaking strain around 2.5 to 4 tons max.

You would need to get the full specification and know how much the builders skimped.

It's possible that the floor would take the weight the heating pipes not so much.

[eggy74]

If it was originally specced to have under floor heating, i would imaging there is a layer of insulation ( Jablight or similar ) between concrete and screed layers which would crush.

[amateur]

Just tell her it's a daft idea.

[sandspider]

Thanks folks. I don't have the full spec, will see if I can find any details amongst the house paperwork. Given the bodging on the rest of the house, I'd imagine some corners may have been cut! Though it is an amdega conservatory, which apparently were good in the day... Sounds like it may not be a wise idea, though it would mean the kids could use the pool for more of the year.

[Old Boggy]

10 hours ago, amateur said:

Just tell her it's a daft idea.

I`m inclined to agree.

If it`s big then it more than likely is going to be near or adjacent to electrical sockets which won`t be very conducive to water splashes. Just a thought.

OB

[JKD]

13 hours ago, eggy74 said:

If it was originally specced to have under floor heating, i would imaging there is a layer of insulation ( Jablight or similar ) between concrete and screed layers which would crush.

Just a slight correction to this,,,, the rigid insulation wouldn't crush, but would depress slightly with that amount of weight on it. If something has got to give, it'll be the concrete 'slab',,,, how much it will 'give/move' is dependent on how the sub-base (oversite, hardcore, sand blinding etc) was prepared and/or if there was re-mesh in the concrete.

I carry out domestic house insurance repairs and subsiding conservatories are not rare, but,,,, it's usually due to poor workmanship, hidden by the 'nice finish'. Combine this with actual subsidence creates some proper horror stories.

10 hours ago, amateur said:

Just tell her it's a daft idea.

I'd just go with this 👍

[Centrepin]

1 hour ago, JKD said:

Just a slight correction to this,,,, the rigid insulation wouldn't crush, but would depress slightly with that amount of weight on it. If something has got to give, it'll be the concrete 'slab',,,, how much it will 'give/move' is dependent on how the sub-base (oversite, hardcore, sand blinding etc) was prepared and/or if there was re-mesh in the concrete.

I carry out domestic house insurance repairs and subsiding conservatories are not rare, but,,,, it's usually due to poor workmanship, hidden by the 'nice finish'. Combine this with actual subsidence creates some proper horror stories.

I'd just go with this 👍

Unlikely to have mesh or any form of rebar in the floor if underfloor heating.

More than likely self compacting concrete onto visqueen over bare earth.

Over the years I've seen many houses and conservatory built, plus many other installations using concrete.

Never unless it was mine or the actual builders own property have I seen anything built to spec.

Corners are cut and money saved, usually on concrete because once laid it's never seen again.

The normal spec for under floor is block with insulation with self compacting concrete poured over. 

More common is block, or hard-core, visqueen, and very wet cheapest concrete poured over. 

Savings on concrete can be over £1K alone. 

For those that don't know, visqueen is a very thick polythene sheet, unfortunately all too often replaced with stuff the thickness of clingfilm. 

Self compacting concrete is specialised concrete with additives and aggregate no bigger than 4mm that once poured levels it's self levelling and sets with little more than a light tamping. It should be around the consistency of emulsion paint and pour the same. Not cheap.

Often replaced by cheap concrete with 10mm gravel (pea gravel) and "brushed or kicked" into place once its been over watered on site. Out of spec and guarantee from the concrete company voided by the builder. 

The breaking strain of this cheap method is often less than a 10th of the actual spec but by then the builder has long gone. The underfloor heating pipes often float to the surface during this process and are pushed down as often as needed untill it's set. Often pipes can be as little as 2mm under the surface but again once the carpet or floor is laid, unseen out of mind.

Basically anything using concrete can be skimped on and usually is, first of all by the company ordering it, then again by the addition of water on site by the builder. Unless you ordered it, and supervised its delivery and lay, it will be out of spec.

[eggy74]

8 hours ago, JKD said:

Just a slight correction to this,,,, the rigid insulation wouldn't crush, but would depress slightly with that amount of weight on it. If something has got to give, it'll be the concrete 'slab',,,, how much it will 'give/move' is dependent on how the sub-base (oversite, hardcore, sand blinding etc) was prepared and/or if there was re-mesh in the concrete.

I carry out domestic house insurance repairs and subsiding conservatories are not rare, but,,,, it's usually due to poor workmanship, hidden by the 'nice finish'. Combine this with actual subsidence creates some proper horror stories.

I'd just go with this 👍

Kpa of Jablite is half that of p.i.r. boards, typically 70 Kpa for Jablite or 10 psi in non metric. As to crush v compress, 10% movement could be up to 15mm. either a cracked slab or a massive gap all the way around under the skirting will be almost certain (its how i make a living too)

[JKD]

48 minutes ago, eggy74 said:

Kpa of Jablite is half that of p.i.r. boards, typically 70 Kpa for Jablite or 10 psi in non metric. As to crush v compress, 10% movement could be up to 15mm. either a cracked slab or a massive gap all the way around under the skirting will be almost certain (its how i make a living too)

The gap round the skirting was my first thoughts as to what would show first, as the pool filled. But, we're all guessing as to the slab's make up 🤷

General advice seems to be "don't do it" !!!

[sandspider]

I've searched through my house paperwork and can't find any info on the conservatory floor at all. Sounds like it would be wiser not to do it.

Many thanks for all the input.😗